Bright copper plating bath containing mixtures of metal compounds



United States. Patent BRIGHT COPPER PLATING BATH CONTAINING lVIIXTURES OF METAL COMPOUNDS Christian I. Wernlund, Niagara Falls, N. .Y., assignor, by mesne assignments, to Elechem Corp., Jersey City, N. J .,a corporation of New Jersey No Drawing. Application October 9, 1956 Serial No. 614,826

6 Claims. (Cl. 204-44) This invention relates to the production of bright copper electrodeposits from aqueous cyanide solutions containing certain metallic addition agents, antimony in particular.

The present application is a continuation-in-part of my copending application Serial Number 352,268, filed April 30, 1953, now abandoned.

As shown in my U. S. Patent No. 2,774,728, trivalent antimony is especially distinguished as an additive in aqueous copper cyanide plating solutions by its ability to produce brilliant, soft, ductile and readily buffable copper deposits. A disadvantage of the antimony is the narrowness of the current density range within which it can produce the desired bright deposits.

A broad object of this invention is to effect improvements in the electrodeposition of copper from aqueous copper cyanide solutions.

A further object is to effect improvement in the electro deposition of copper from aqueous cyanide solutions containing a metallic brightening agent.

Another object is to extend the bright plating range of aqueous cyanide solutions containing a metallic brightening agent. 7

A specific object is to provide an aqueous bath containing copper cyanide and trivalent antimony and possessing an improved bright electroplating range.

The above-mentioned and still further objects are achieved in accordance with this invention by electrodepositing copper from a cyanide bath containing both a primary metallic addition agent, usually antimony, and

TABLE.-OONCENTRATION BRIGHTEN'ERS WHEN USED are added. Preferred are potassium baths containing, in aqueous solution:

The free cyanide is that measured by the liebig silver nitrate titration.

The cheaper sodium compounds are frequently substituted in whole or in part for potassium compounds. Since the potassium formulations permit higher rates of copper deposition and produce slightly brighter deposits, they are technologically preferred.

Antimony, the preferred primary brightener of the invention, may be added to the basic solution in almost any of'its soluble trivalent forms. Antimony trioxide, potassium antimonyl tartrate, and many other compounds may alike be used. The quantity of antimony employed may vary between about 0.010 and 0.20 g./ 1., considered as the metal, with about 0.050 and 0.10 g./l. preferred.

The weight of the antimony compound supplying this desired weight of antimony may, of course, be readily determined from the appropriate gravimetric factors.

In addition to the preferred antimony, several other metals may serve as the primary brightener of this invention. These metals are bismuth, mercury, silver and cadmium. While they may be supplied as many of their soluble compounds, representative compounds and weights are given in the table below. I

The secondary brighteners of the invention are zinc, arsenic, cobalt, iron and cadmium. The anomalous appearance of cadmium as both a secondary and a primary brightener is due to the fact that it exhibits improved results when employed with any othermember of either of the brightening groups disclosed.

The secondary brighteners may also be supplied to the bath in about any convenient soluble compound. Representative compounds and Weights are included in the table below along with the same data for the primary brighteners.

Weight of Metal Weight of Metal Compound Added Compound Efieetive Preferred (g.ll.)

( -lL) (gJL) 0. 010-0. 20 0. 050-0. 10 KsbO-C4H40lry2H2O 0. 03-0. 5 0. 002-0. 05 0. 002-0. 01 BR0511900371320 0. 01-0. 2 0. 008-1. 0. 008-0. 08 Hg(ON)z 0. 01-2. 0 0. 008-1. 62 0. 008-0. 08 AgGN 0. 01-2. 0

0. 007-7. 00 0. 070-3. 50 Cd(CN)z 0. 01-10 0. 056-2. 32 0. 120-1. 65 Zn(CN) 0. 10-4. 0

0. 760-7. 60 0. 760-8. A8203 1. 00-10. 0 0. 003-0. 32 0. 016-0. 16 K400 (0N)s 0. 02-2. 0 0. 088-0. 40 0. -0. 36 K4Fe(ON) 0. 50-2. 3

also a secondary metallic agent synergistically cooperative with the primary in forming bright copper deposits. The secondary agents of this invention are cobalt, iron, arsenic, cadmium, and zinc.

Almost any substantially conventional aqueous copper cyanide plating solution may be employed as the basic baths to which the metallic brightcners of this invention The compounds cited in the table as yielding the desired metallic additive are intended as purely illustrative and not as sharply restrictive. In general any compound of the particular additive can be utilized that is compatible with the bath being employed, i. e., is soluble in the bath and does not change important bath characteristics such as the pH. The weight of compound Patented Nov. 4, 1958 added,,will be that. necessary .to give .aweight ofthe desired metal within the range designated as elfective.

The modified baths of this invention, like many cyanide copper baths, may yield rough plate unless precautions are taken thereagainst. Conventional anti-pitting agents are therefore generally also added to the baths; Satisfactory anti-pitting'agents are the betaines, e. g., C-decyl betaine, of the type shown by Holt, U. S. Patent 2,255,057.

Operational conditions for the present electroplating process are substantially those of the prior art. Thus a temperature of about 60-95 C. may be employed, about 80 C. being preferred. Agitation as by stirring may be employed. Choice of cathodes or workpieces is optional. The usable current density range is broader than that. of unmodified baths, bright copper plate being obtained at up to 60 a./s. f. (amps/ft?) or above in some instances. I

There follow some examples which serve to illustrate, but not to limit, the invention in more detail.

Example 1 This example shows the synergism of antimony and cobalt in aqueous copper cyanide plating solution.

(a) An aqueous copper plating solution was made up with the following composition: 14 oz./gal. of cuprous cyanide, 1 oz./gal. of free potassium cyanide, oz./gal. of potassium hydroxide, and 0.67 oz./gal. of an anti-pitting agent comprising about 30% by weight of trimethyl benzyl ammonium chloride and 12.5% of C-decyl betaine, the remainder being water.

Plating was carried out from this conventional solution under the following conditions:

Plating tank 1000 ml. oscillating cathode Hull cell. Cathode area 20 in. Cathode current density (front side) 30-34 a./s. f. Rate of stirring 12 ft./min. Temperature 80 2 C.

No bright plate was obtained from this bath above a./s. f.

(b) To the basic plating solution of (a) were added 5 g./l. of potassium cobaltocyanide, K Co(CN) and plating carried out as before. Bright copper plate was obtained solely in the 17-25 a./s. f. current density range.

To another sample of the solution of (a) was added 50 p. p. m. of antimony as potassium antimonyl tartrate. In this particular instance bright plate was produced only between 14 and 23 a./s. f.

When plating was accomplished from a sample of the bath of (a) containing, the cobaltocyanide and 50 p. p. In. of antimony from the antimonyl tartrate, very bright plate was obtained in the 11-44 .a./s. f. range.

This plate was noticeably brighter than thatobtained with either of the additives alone.

Example 2 The runs of Example 1 were substantially repeated except that 15 g./l. of potassium ferrocyanide,

were substituted for the cobaltocyanide. The ferrocyanide alone gave bright plate only in the 22-34 a./s. f. range. When combined with 50 p. p. m. of antimony, very bright plate was obtained from 17 to 45 a./s. f. ThepIate obtained withthe dual additives was, as before,t noti ceably brighter than that obtained with either alone,

- Example 3 up containing 14 oZ./gal. of cuprous cyanide, 2.0 oz./

gal. of free sodium cyanide, 6.0 oz./gal. of free potassium hydroxide, 1.5 oz./gal. ofsodium carbonate, and the anti-pitting agent of Example 1. This bath, unrnodified,..produced no bright copper above 10 a./ s. f.

A portion of the sodium bath containing 0.025 g./l. of antimony added as potassium antimonyl tartrate showed a .very brightplatingv range-between 13 and 21 a./s. f. and a semi-bright to a definite dull range atl25 a./s. f. and above.

A bath carrying 0.5 g./l. of arsenic trioxide as the sole metallic additive showed a very bright plating range between 20 and 32 a./s. f., hazy bright between 18 and 20 a./s. f. and dull elsewhere.

A bath containing both antimony and arsenic, in the.

quantities utilized separately, showed a very bright low current density plating range between 8 and 36 a./s. f., a semi-bright range up to 50 a./ s. f. and adull range above 50. The combination of additives therefore produces a' single bright plating band acceptable both as regards brightness and current density range.

Example 4 This example shows the joint effect of cadmium and antimony in copper cyanide baths.

Copper was electrodeposited from the basic sodium cyanide bath of Example 3 containing additionally- 1,0

g./l. of cadmium cyanide and 0.095 g./l. of antimony trioxide. A bright plating range of 15-44 a./s. f. resulted. Antimony trioxide alone in a sodium cyanide bath gave a bright range of 9-18 a./s. f. .Cadmium alone gave bright plate in the 35-52 a./s. f.- range.

Example 5 This example shows the joint effect of zinc andantimony in copper cyanide baths. V The experiments of Examples 3 and 4 were substan-. tially repeated with 2.0 g./l. of zinc cyanide and0.050 g.'/l. of antimony trioxide as the additives.

was producedin the 9-38 a./s. f. range. Zinc cyanide additive alone gave bright plating ranges of 26-40 and trioxide alone gave abright 50-60 a./s. f. Antimony range of 9-18 a./s. f.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An aqueous bath for electrodepositing bright copper containing about 5-20 oz./gal. of copper cyanide, about 0.010-0.20 g./l. of trivalent antimony supplied as a soluble salt thereof, and about 0.120-1.65 g./l. of zinc.

3. An aqueous bath for electrodepositing bright copper containing about 5-20 oz./ gal. of copper cyanide, about 0.0100.20 g./l. of trivalent antimony supplied as a soluble salt thereof, and about 0.760-3.80 g./l. of arsenic.

4. An aqueous bath for electrodepositing'bright copper-1 containing about 5-20 oz./ gal. of copper cyanide, about 0.0100.20 g./l. of trivalent antimony supplied as a soluble salt thereof andabout 0.016-0. 16 g./l. of cobalt.

5. Anaqueous .bathfor electrodepositing bright containing about 5-20 oil/gal. of copper cyanide, about Bright plate 5 6 0010-020 g./l. of trivalent antimony supplied as a soluble 1,120,795 Daft Dec. 15, 1914 salt thereof, and about (1180-036 g./l. of iron. 1,559,077 Lattl'e et al. Oct. 27, 1925 6. An aqueous bath for electrodepositing bright copper 2,737,485 Overcash et a1. Mar. 6, 1956 7 containing about 5-20 oz./ gal. of copper cyanide, about 0.010-0.20 g./l. of trivalent antimony supplied as a soluble 5 OTHER REFERENCES Salt thereof and about of cadmlum- Ernst et al.: Transactions Electrochemical Soc., vol.

References Cited in the file of this patent 61 (1932) 391-394 UNITED STATES PATENTS 10 1,120,794 Daft Dec. 15, 1914 

1. AN AQUEOUS BATH FOR ELECTRODEPOSITING BRIGHT COPPER CONTAINING ABOUT 5-20 OZ./GAL. OF COPPER CYANIDE, ABOUT 0.010-0.20 G./L. OF TRIVALENT ANITOMY SUPPLIED AS A SOLUBLE SALT THEREOF, AND A METAL CHOSEN, IN THE RESPECTIVE PROPORTIONS SPECIFIED, FROM THE GROUP CONSISTING OF: 0.0562.32 G./L. ZINC, /.ML/-7.60 G./L. OF ARSENIC, 0.003-0.32 G./L. OF COBALT, 0.088-0.40 G./L. OF IRON, AND 0.007-7,00 G./L. OF CADMIUM. 